The invention relates to a process and an installation for the production of aromatic compounds that operates in a fixed catalyst bed.
The invention pertains to, for example, aromatization reactions, i.e., production of aromatic hydrocarbons (benzene, toluene, xylenes) or to reforming reactions.
The catalysts that are generally used contain at least one noble metal, generally platinum, that is deposited on the alumina, as well as at least one promoter metal that is generally rhenium. These catalysts have been extensively described in literature.
Patent FR-2,373,602 thus describes a catalyst that contains an alumina substrate, 0.05 to 0.6% by weight of platinum, 0.02 to 2% by weight of rhenium, 0.05 to 3% by weight of thallium or indium, and 0.1 to 10% by weight of a halogen (generally chlorine).
U.S. Pat. No. 4,722,780 shows a reforming process in which the feedstock moves successively onto two types of fixed beds of two different catalysts. Each catalyst contains platinum and rhenium and optionally an additional metal that is selected from tin, germanium, lead, indium, thallium, and titanium. Catalyst A of the first type of bed (traversed by the feedstock) exhibits an Re/Pt ratio by weight that is greater than the Re/Pt ratio by weight of catalyst B of the second type of bed, and catalyst B contains at least 0.08% by weight of rhenium (relative to the substrate).
In this type of scheme, it thus is possible to use a catalyst according to Patent FR-2,373,602, in particular in the second type of bed. Other catalysts that contain 0.01 to 3% of additional metal, as U.S. Pat. No. 4,722,780 indicates, are also suitable.
Furthermore, whereby the industrial use of such processes is expensive, systems have been developed that make it possible to increase the volumes and the masses of catalyst that are loaded for the same reactor.
U.S. Pat. No. 5,202,097 thus proposes a device that is placed above the catalytic packing. The device comprises a cloth layer that is made of a suitable material that essentially completely covers the packing. Inert balls are placed on this cloth layer to ensure that the cloth layer is held. As this document shows, this device prevents dead zones at the top of the reactor and makes it possible to increase the amount of catalyst in the reactor.
With a view to the same goal of saving catalytic mass, a so-called compacted loading technique, described in Patent FR-2,646,399, was developed, and said technique makes it possible to increase the amount of solid that is introduced in a certain volume.
Means for optimizing the installation in terms of energy were also developed, for example heat exchangers are used on the fluids outside of the reactors. Exchangers that are marketed by the Packinox Company and that are used generally in this field will be cited.
Each of these techniques, to date used separately, was able to provide improvements.
It has now been discovered, quite surprisingly, that the combination of these techniques used in a process for production of aromatic compounds makes it possible to obtain a synergy whose results go beyond those expected. As a result, the capacity of the installation can be increased by close to 10% by maintaining the yield of reformate and its quality without increasing the wear of the catalyst, and even in a preferred case, the cycle length of the catalyst is increased.
More specifically, the invention relates to a process for the production of aromatic compounds in which the feedstock moves through at least one fixed bed of a catalyst that contains at least platinum and at least 0.08% by weight of rhenium (relative to the substrate), a process in which the fixed beds are arranged in at least one reactor, and in which, before being introduced into the first fixed catalyst bed, the feedstock that is to be treated undergoes a heat exchange with the effluent that is obtained from the last fixed catalyst bed, whereby the heat exchange is carried out with a pressure drop that is less than 1 bar and a temperature difference of at most 70xc2x0 C.
More particularly, the invention relates to a process for the production of aromatic compounds in which the feedstock moves successively through at least two fixed catalyst beds that contain at least platinum and rhenium, and catalyst A of the first bed or beds (in the direction of circulation of the feedstock) exhibits a ratio by weight of the Re/Pt metals that is greater than the ratio by weight of the Re/Pt metals of catalyst B that is contained in the last bed or beds, a process in which the fixed beds are arranged in at least one reactor and in which, before being introduced into the first fixed catalyst bed, the feedstock that is to be treated undergoes a heat exchange with the effluent that is obtained from the last fixed catalyst bed, whereby the heat exchange is carried out with a pressure drop that is less than 1 bar and a temperature difference of at most 70xc2x0 C.
At least one radial fixed bed that is located at the top of the reactor is preferably covered by a cloth layer.
The catalyst is therefore in the form of one or more fixed beds in one or more reactors. According to the invention, a single type of catalyst can be used (catalyst B); it can be preceded by another catalyst that is advantageously the catalyst of type A; and it can also be followed by another catalyst for this process.
When a single fixed catalyst bed B is used, the feedstock undergoes a heat exchange with the effluent that is obtained from this bed.
If several fixed beds are used (of A, B or any other catalyst), the feedstock, before entering the first bed, has undergone a heat exchange with the effluent that is obtained from the last bed.